A zd1211 USB WiFi (ZyDAS chipset) adapter was tested with success using zd1211rw firmware (1.3) on a WPA secure network (wpa_supplicant-0.5.7).
The system works fine in 802.11b only 'cause it's USB 1.1 .
root@efika:~# iwlist scan
eth0 Interface doesn't support scanning.
lo Interface doesn't support scanning.
dummy0 Interface doesn't support scanning.
eth1 Scan completed :
Cell 01 - Address: 00:13:64:17:63:1A
ESSID:"<hidden>"
Protocol:IEEE 802.11bg
Mode:Master
Channel:7
Encryption key:on
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 6 Mb/s; 9 Mb/s
11 Mb/s; 12 Mb/s; 18 Mb/s; 22 Mb/s; 24 Mb/s
36 Mb/s; 48 Mb/s; 54 Mb/s
Quality=100/100 Signal level=100/100
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
Extra: Last beacon: 1436ms ago